A. Field of the Invention
This invention relates to the wet spinning process for producing yarn of copolymers consisting essentially of recurring units of the formulas ##STR1## and ##STR2## where Ar is ##STR3## R is a C.sub.1 to C.sub.4 alkyl and the mole ratio of (a) units to (b) units is between 20:80 and 95:5. More specifically, the invention relates to the improvement of applying a certain zirconium-containing finish to the yarn during the wet spinning process whereby the twist efficiency of such yarn is significantly increased. The term "twist efficiency", as used herein means the ratio, expressed as a percentage, of the tenacity of a cord plied from strands of a given yarn to the tenacity of a single strand of the yarn, i.e. ##EQU1## The terms "O/H COPOLYMER", "O/H YARN" and "O/H CORD" are used herein to refer to the above-described copolymer, yarn thereof, and cord formed from yarn thereof, respectively.
B. Description of the Prior Art
There is a continuing demand in the tire industry for the development of a higher tenacity cord for use in the carcass of a tire. Yarns of organic polymers (e.g. nylons and polyester) are presently used in forming carcass cords. The cords are formed by plying two or more twisted strands of the yarn to provide a highly twisted configuration having tenacities in the 7 to 10 grams per denier range; the highly twisted configuration of the cords is necessary for good fatigue resistance properties. O/H YARN has a relatively high tenacity when compared to that of either nylon or polyester yarn. However, cord formed from twisted strands of O/H YARN although having good fatigue resistance has a much lower tenacity than expected due to the poor twist efficiency of O/H YARN. Normally, yarns have twist efficiencies of at least 65% (nylon 66 is .gtoreq. 72%), whereas in the case of O/H YARN its twist efficiency is .ltoreq. 50%.
Accordingly, it is an object of this invention to increase the twist efficiency of O/H YARN.
Another object of the invention is to provide a high tenacity cord suitable for use in the carcass of tires.
Other objects and advantages of the invention will become apparent from the following detailed description thereof.